Never used it myself, but apparently www.sitepoint.com is the best website, although that costs money. If you want to get 100% of the money you sell for, then sell here on DP in the Buy, Sell and Trade section!
Sitepoint is sure will help you selling domains, but I prefer to sell domains at dnforum.com (domain name forum)
namepros and DP are good if you dont want to pay for membership else you can opt for sitepoint or dnforum
the best will always be having "this domain for sale" in your whois info. the leads convert best from those emails.
If you can wait, just post it as available at SEDO and others. If you need to sell it fast, then Namepros and DP forum are fine - but you are unlikely to get top dollar. For certain types of names, Ebay can also be very good. The buyers are less informed about domain values, but will usually jump at obvious keyword (DVD, loan, insurance) or highly brandable domains.
DP is always a good place as is namepros and DNforum, there is also sedo, ebay and sitepoint. So u have enought to chose from.
There's no such place as the best, you've just gotta try different places. Try places like DP, Namepros, DNForum, Domainstate, Sedo, Afternic, Moniker auctions, etc.
It really depends on the level of the domain. For large domains, I use sedo. If it is a quick flip on a domain, dp, and if I don't get great results, i try ebay. I've used sitepoint, but you have to have very nice name there. Ebay is a STRANGE place for domains. I've sold domain on ebay for $80 that I couldn't sell on dp or sitepoint for $20. I've also sold domains on ebay for $8 that I thought could sell for over $100.